Objective   Changes in soil enzyme activities and ecoenzymatic stoichiometry of the degrading Hylocereus undatus forests in karst rocky desertification areas were investigated.

  Method  Pitaya growing areas with varying degrees of degradation, i.e., no degradation (ND), light degradation (LD), moderate degradation (MD), and severe degradation (SD), were targeted for the study. One-way ANOVA, two-way ANOVA, Pearson's correlation analysis, and redundancy analysis (RDA) were conducted to analyze the variations on the activities of β-glucosidase (βGC), N-acetyl-β-D-glucosidase (NAG), leucine aminopeptidase (LAP), and acid phosphatase (ACP) as well as the ecoenzymatic stoichiometry in 0–30 cm soil layers at the sampling areas.

  Result   (1) Among the soil enzymes, βGC and ACP generally increased followed by a decline with increased degree of degradation. NAG differed significantly only in the soils in 10–20 cm and 20–30 cm layers. LAP was greater in SD and MD than ND area. In general, the LAP+NAG activities increased with the progress of degradation. (2) Soil enzyme C:N decreased with increasing degradation, but the ratios of C:P and N:P increased to some extent, indicating changes occurred on resource utilization by the degraded pitaya forest. As the degradation deepened, the vector L of ecoenzymatic stoichiometry enlarged to maximize in MD; the vector A decreased to bottom out in SD; and all vectors A remained less than 45°, which suggested that the microbial growth in soil was restricted by N availability. (3) An RDA analysis indicated that the soil physicochemical properties could explain 83.4% of the variation in soil enzyme and ecoenzymatic stoichiometry, and that AP and TN were the key factors that covered 47.5% and 24.3%, respectively, of the variation.

  Conclusion   The microorganisms in soil of degraded H. undatus forests in karst rocky desertification areas were N-limited. Such nutrient restriction further aggravated the degradation. Conceivably, the enzyme activities and ecoenzymatic stoichiometry of the degraded pitaya forest soil could be remedied and rejuvenated by proper N and P fertilization.